What are emerging contaminants and how to remove them from wastewater

What are emerging contaminants ? You've probably asked yourself this question before. The first thing to explain is that their name is somewhat misleading, as these contaminants haven't recently arrived in our waters. They aren't new substances; they are compounds that we are already able to identify and measure thanks to the advances in analytical chemistry in recent years. It is precisely this quantification that has led to concerns about their environmental consequences and how they affect the health of living beings that are directly impacted by them.

But what do we mean by emerging water pollutants or pollutants of emerging concern ? Their definition is still not entirely clear. Among the compounds that make up this group, we find, basically, pollutants whose origin is linked to human activity, such as agriculture and livestock farming, or lifestyle , among others. This factor leads to their presence in wastewater.

We are talking about pharmaceuticals ; such as antibiotics, anti-inflammatories, antifungals, photoprotectors, hormonal medications, antidepressants, or for diabetics; pesticides , such as fungicides, insecticides or herbicides; industrial derivatives , where metallic nanoparticles, microplastics, industrial additives, plasticizers or flame retardants stand out; and also those that come from the manufacture and use of creams , lotions, detergents, hygiene and cleaning products, or derivatives of the consumption of illegal drugs.

As you can see, the list is extensive and difficult to classify. That's why the European Commission publishes a Watch List every two years, updating and listing emerging contaminants that each Member State must analyze. Based on the data collected, an assessment is made as to whether these should be included in the Priority Substances List.

How can we remove emerging contaminants from wastewater?

Wastewater treatment follows very strict criteria that guarantee processes such as its return to the environment or reuse. However, given the constant emergence of new analytical criteria, we can highlight two main areas. First, detection; and second, processes that drastically reduce the presence of these contaminants or directly eliminate them from wastewater, thus preventing any environmental impact.

Many of these pollutants, in large volumes, are known to have adverse effects on living species, as they act as endocrine disruptors . They can affect the reproductive system and fertility of certain animal species , increase malformations and mortality in fish, limit the growth of certain algae, or even be directly toxic to some varieties (among other harmful effects). Hence the importance of studying their hazards and analyzing the maximum concentration to limit their negative effects on the environment and biodiversity.

As we mentioned, there are various processes for reducing its concentration, which can be found in Wastewater Treatment Plants (WWTPs ). These technologies are basically the following: physical processes , including membrane technology (microfiltration, ultrafiltration, nanofiltration, and reverse osmosis ) and activated carbon adsorption ; biological processes , such as membrane bioreactors; and chemical processes, such as advanced oxidation processes. Of all these technologies, advanced oxidation processes and membrane treatment, specifically reverse osmosis, provide the best results obtained to date.

The membrane acts as a physical separation barrier; it does not destroy the compounds themselves. Thanks to this technology, we obtain two streams: a "purified" stream with a low concentration of emerging contaminants, and a "concentrated" stream with a high concentration of these contaminants.

If we want to destroy these pollutants, we must use advanced oxidation technologies, which currently present some drawbacks, such as the generation of byproducts and high energy and reagent consumption. Hence the need for continued research to develop a technology that is efficient in all aspects of destroying these pollutants.

Patricia Negro, head of the Technological Development area at SITRA, concludes that “emerging contaminants are a health risk, hence the vital importance of working towards safe regulations that go hand in hand with technological advances that allow us to achieve these objectives efficiently . ”